In the technology examined by the inventors of the present invention, for example, in the electron beam writing system used in the manufacture of a semiconductor integrated circuit device (LSI), the LSI has been increasingly miniaturized, the structure thereof has become complex more and more, and the capacity required for the pattern data has been increased. Therefore, the improvement of the writing accuracy and the improvement of the writing throughput have been demanded. For its achievement, in addition to the electron beam writing system using the variable shaped beam, the electron beam writing system using the character projection exposure in which the mask pattern is transferred through a reducing projection has been developed.
Also, as the next-generation lithography system, the development of the electron beam projection lithography represented by the EPL (Electron Projection Lithography) and the electron beam writing system using multiple beams in which multiple electron beams are simultaneously deflected and turned on/off depending on the exposed/non-exposed parts of a semiconductor wafer in the writing has been proceeding.
In any electron beam writing systems, it is necessary to measure the electron beam current to correct the dose of electron beam irradiation in the writing. The accurate control of the dose of electron beam irradiation leads to the improvement of the dimensional accuracy of the pattern. Therefore, the accurate measurement of the beam current of electron beam to be a standard for determining the irradiation dose is indispensable to perform the accurate writing.
As an example of the electron beam writing system, the electron beam writing system in which the electron beam is pulsed and the writing pattern is formed while controlling the pulse width during the beam-on time is known. The electron optical apparatus of this electron beam writing system is comprised of an evacuated vacuum column, an electron gun for generating electron beam, lens for focusing the electron beam, a blanking electrode and a blanking aperture for turning on/off the electron beam, an electron beam detecting device for measuring the beam current of the electron beam, a movable stage on which a sample to form a writing pattern is mounted, a deflector for determining a position of the electron beam on the stage, a cable terminal for leading the wiring system to the air and others.
In the electron beam writing system described above, the electron beam generated from the electron gun is focused and deflected by the lens and the deflector and then reaches the electron beam detecting device and the sample on the movable stage. During the beam-off time, the electron beam is deflected by the blanking electrode and is irradiated to the blanking aperture to block the electron beam. By applying the pulse voltage to the blanking electrode, the electron beam is turned on/off to generate the pulse beam.
By the control system of the electron beam writing system, the generated electron beam and pulse beam are irradiated to the electron beam detecting device. The signals detected by the electron beam detecting device are transferred to a measurement circuit through a detected signal line. Based on the measurement result, the amount of beam current of the electron beam is calculated. Then, the beam-on time in the writing is corrected based on the measurement data of the calculated amount of beam current. In this manner, the writing by the desired irradiation dose can be performed. Note that, in the electron beam writing system using the variable shaped beam, based on the measurement result of the beam current, the area of the electron beam is corrected to control the irradiation dose.
In the conventional beam current measurement, for example, as described in the Japanese Patent No. 3082662, a Faraday cup is used as an electron beam detecting device and an ammeter is used as a measurement circuit so as to measure the current value or the current density.
Also, as a method for correcting the dose of the electron beam irradiation, the technologies described in Japanese Patent Laid-Open Publication No. 5-299328 and No. 2003-51437 are known.